The invention relates to a unit fuel injector of the type with an open injector, comprising an injector body with an axial space, which ends in an injector cap with injection bores, comprising an injection plunger guided in the axial space and serving as a closing-off element, which injection plunger bounds in the axial space a pressure space from which the injection bores extend.
A unit fuel injector of the type with an open injector is known, for example, from EP 460 693 A1. It has the special feature that the injection plunger is a pumping element and closing element at the same time. These unit fuel injectors also have the problem when they are used in high-power diesel engines--which are usually supercharged--with respect to the minimizing of consumption and emissions that the injection requirements differ considerably between idling and full load.
During idling and at low compression pressure, the rate of injection is low and the ignition delay is long. During the ignition delay, as little fuel as possible is to be injected as slowly as possible, and nevertheless atomized well. At full load and a high engine speed, on the other hand, the rate of injection is great--in the case of supercharged high-power engines even particularly great--and the duration of injection is to be as short as possible, since only a limited crank angle is of course available for the injection. All in all, optimizing combustion with regard to consumption and emissions requires a uniform distribution of the fuel in the combustion chamber and defined atomization.
The greater the differences in rates and speeds, the more difficult it is to optimize combustion with constant injector cross sections. Although it is known from EP 470 348 A1 and DE 44 32 686 C2 to provide a number of rows of injection bores and two concentric plunger needles in unit fuel injectors, in which the pumping element and closing element are separate, in order in this way to be able to adapt the cross section of the injector to the operating state, these solutions concern only the valve function and consequently cannot be transferred to the open unit fuel injectors of the generic type. Due to their special structural design, there is a different relationship between the cross section of the injector and the injection pressure.